With Iraq's second-largest city, Mosul, firmly under its control, the militant group the Islamic State in Iraq and Syria is threatening the takeover of more cities, including the capital, Baghdad. "Continue your march as the battle is not yet raging," ISIS spokesman Abu Mohammed al-Adnani purportedly said in an audio recording posted early Thursday on the group's media website. "It will rage in Baghdad and Karbala. So be ready for it." CNN cannot confirm the authenticity of the 17-minute-long audio or the time of its recording.